1. Field of the Invention
The present invention relates to a door assembly in which movement of an inner secondary door formed within the structure of a larger, primary door, is controlled when opening and closing the larger door.
2. Description of the Prior Art
There are numerous situations in which a door assembly requires a certain versatility so that a full length door can be opened and shut on some occasions, but wherein only a portion of the door can be opened and shut on other occasions. One conventional device of this type is known as a Dutch door. A Dutch door is a door mounted within a frame and divided into upper and lower portions which are rotatable independently of each other about separate hinges vertically aligned with each other along a hinged edge of a door frame. The upper and lower portions of a Dutch door can typically be latched together by any conventional latching mechanism, such as a slide bolt. When the door portions are latched together, the entire door rotates as a unit about the single hinge axis located at the hinging edge of a door frame. Alternatively, the upper and lower sections can be unlatched from each other, so that the lower portion of the door can be latched shut while the upper door portion is opened. When located in an exterior wall of a building, a Dutch door provides the building with ventilation and approaching visitors can be easily observed.
A Dutch door construction is somewhat lacking in versatility, since the upper portion of the door which can be opened relative to the lower portion extends entirely across the width of the door frame. As a consequence, when the upper door portion is opened While the lower door portion remains shut, the occupant of the building is provided with relatively little security. Any intruder need merely reach through the opening within which the upper portion of the Dutch door moves and unlatch or unlock the lower door portion, thereby gaining unrestricted access to the building.
Another type of door structure in which the door is divided into separately openable portions involves the formation of a relatively small opening within a larger, primary door in which a smaller, hinged window is located. The small window can be opened while the larger, surrounding door remains shut, thus allowing an occupant of a building to view anyone standing outside of the door. Because the window is quite small, an intruder cannot reach through the window and unlatch the larger door within which the window is formed. However, because the window is quite small, the view afforded to the occupant of the building is rather limited. Furthermore, due to its small size, the window provides an opening of very limited size through which very little fresh air and few cooling breezes may pass.
The problem of limited visibility and inadequate fresh air can be solved by merely making the window opening larger, to the extent that the window hinged to the structure of the main door itself forms a smaller, secondary door within the larger, surrounding primary door. However, in a conventional door assembly of this type the relatively large size of the secondary door can cause damage to the building if it is inadvertently left open while opening the larger, main or primary door. That is, if the larger, primary door is opened while the smaller, secondary door mounted in an opening therewithin remains open, the smaller door can swing arcuately in an articulated manner and the free edge of the smaller door can gouge an interior wall surface due to its uncontrolled swing when the primary door is opened.
Also, even when the primary door is closed, the secondary door is subject to being blown by the wind back against an adjoining wall surface due to the substantial size of the secondary door. Furthermore, because the secondary door is able to swing so widely relative to the moving plane of the primary door as the primary door itself is opened, the secondary door can often strike the interior wall surface within a building with sufficient force to shatter any glass panes that may be mounted in the secondary door. In addition, the swing of the secondary door within the room is relatively unpredictable, so that a room occupant standing close to the door can be injured by the uncontrolled swinging secondary door as the primary door is opened. Therefore, in conventional secondary doors of this type it is essential for the secondary door to be closed and latched relative to the primary door each time the primary door is opened.